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ARP 2600 VCO
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wintermute303



Joined: Sep 08, 2009
Posts: 3
Location: Germany

PostPosted: Tue Sep 08, 2009 5:46 am    Post subject: ARP 2600 VCO Reply with quote  Mark this post and the followings unread

Hi there,

I am new to this board but have been reading posts for a while.
I started a small ARP 2600 project inspired by Andy and his great dual odyssey VCO clone. Now I have some questions regarding the ARP 2600 VCOs since they seem to be different from the Odyssey ones.
As far as I understand the odyssey uses 0 to 6 Volts for the saw wave and 0 to 5 Volts for the square while the 2600 has 10 Volts peak to peak. I simulated the ARP 2600 circuit and found the Voltage of the saw to be 0 to 10 Volts. Can anyone verify this to be correct? After doing some research I thought the 2600 VCO centers around 0 with +5 to -5 Volts. I am confussed Confused ...please help.
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AndyR1960



Joined: Feb 16, 2007
Posts: 279
Location: Manchester UK
Audio files: 5

PostPosted: Tue Sep 08, 2009 9:54 am    Post subject: Re: ARP 2600 VCO Reply with quote  Mark this post and the followings unread

wintermute303 wrote:
I simulated the ARP 2600 circuit and found the Voltage of the saw to be 0 to 10 Volts. Can anyone verify this to be correct? After doing some research I thought the 2600 VCO centers around 0 with +5 to -5 Volts. I am confussed Confused ...please help.


The saw output from the 2600 VCO module is 0-10v. For VCO 1 & 3 this signal is sent to the Square/Pulse converters which also output 0-10v.

The saw output from VCO 2 goes to the wave shapers which gives you Square/PWM 0-10v, Triangle +/-5v and sine +/- 5v.

But basically the core VCO's for the 2600 and MKII/III Odysseys are the same, except for a few resistor value changes.

I've just completed an Odyssey VCO using discrete transistors (I have loads of spare 3904/06's hanging around), and works just as well as using the CA3086, and takes up less room!
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wintermute303



Joined: Sep 08, 2009
Posts: 3
Location: Germany

PostPosted: Tue Sep 08, 2009 12:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Andy,

thanks for your reply. So what I tried today was to get the saw-wave to 0-10Volts using the level shifter you posted in another thread. I was able to raise the wave but when I use is as input for the wave shaper board of the 2600 I have no chance to get a -5 to +5 Volts Sine or Triangle. If I use a 5 Volts saw signal I am able to get 10Vpp for the sine but only about 5Vpp for the triangle. The sine also does not sound like a clean sine wave and the triangle has a little spike on top. Is there something wrong circuitwise or is it the input signal? Do you know which resistors I should change to convert the odyssey VCO to a 2600 one? Thanks for your advise.

(By the way I am able to get a clean sine wave but only when ignoring tuning to 10Vpp...its more like -7.5V and and 2.5V)
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isak



Joined: Dec 13, 2009
Posts: 690
Location: Israel
Audio files: 18

PostPosted: Wed Jun 11, 2014 11:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi there.

Did you manage to fix the Tri spike problem?
I'm having the same problem.
See the next link please:
http://www.electro-music.com/forum/topic-59728-25.html


cheers,
Isak E.

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steffensen



Joined: Jul 11, 2012
Posts: 93
Location: Sweden

PostPosted: Thu Jun 12, 2014 1:56 am    Post subject: Reply with quote  Mark this post and the followings unread

The Tri is suppose to look like that. Also, the Sine is pretty much a Tri with rounded corners if you use the 2N3954.
However, if you match up 2x 2N5459's instead, it can be made in to a pretty decent Sine.
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isak



Joined: Dec 13, 2009
Posts: 690
Location: Israel
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PostPosted: Thu Jun 12, 2014 3:24 am    Post subject: Reply with quote  Mark this post and the followings unread

hi steffensen.

i have a perfect sine wave.
what bothers me is the tri top spike going inside the tri.
have you seen the pics?

this is before trimming:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

this is after trimming:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

you say the top spike of the tri suppose to look like that?
i dont mind if it look like that but i can hear it, thats annoying!
its not a pure Tri sound, the small spike is hearble.

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steffensen



Joined: Jul 11, 2012
Posts: 93
Location: Sweden

PostPosted: Thu Jun 12, 2014 3:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi there Isak Wink
Yes, thats how the 2600 Tri looks like indeed. Part of its sound, which i love!
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isak



Joined: Dec 13, 2009
Posts: 690
Location: Israel
Audio files: 18

PostPosted: Thu Jun 12, 2014 3:36 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks man Smile

BTW the THeff design is like the original 2600 VCO schematics.
i followed the scheme and his PCB design.
he he only replaced the single opamp LM301 with dual opamp for the wave shapes as well as the transistors like Andy did in his design.
and your right, amazing sound!
Very Happy

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